The present invention relates generally to the switching of optical signals, and more particularly, to an optical switch with a geometry based on perpendicularly oriented planar lightwave circuit switches.
There are an ever-growing number of new applications that use high bandwidth digital and analog electro-optic systems. For example, in digital computing systems, electro-optic systems are often utilized to route signals among processors. In analog systems, electro-optic systems are often utilized in applications, such as phased array radar. Electro-optic systems are also commonly found in applications that switch high bandwidth optical carriers in communication systems.
In these systems, light beams are modulated in a digital and/or analog fashion and are used as xe2x80x9coptical carriersxe2x80x9d of information. There are many reasons why light beams or optical carriers are preferred in these applications. For example, as the data rate required of such channels increases, the high optical frequencies provide a significant improvement in available bandwidth over conventional electrical channels, such as those channels formed by wires and coaxial cables. Moreover, the energy required to drive and carry high bandwidth signals can be reduced at optical frequencies. Furthermore, optical channels (e.g., waveguides and optical fibers) and even those channels propagating in free space can be packed closely and even intersect in space with reduced crosstalk between channels.
An important component in these systems is the optical cross-connect (OXC) switch. Optical crossconnect switches can be divided into two general classes: 1) those with all-optical switch fabrics, and 2) those with optoelectronic switch fabrics. All-optical switch fabrics do not perform any optical-to-electrical conversion of the optical signals to be switched, whereas optoelectronic switches do perform optical-to-electrical conversion of the optical signals to be switched. The lack of electrical conversion allows all-optical switch fabrics to support bit rates (e.g., bit rates in the 40 Gb/s range and higher), which are beyond the reach of most optoelectronic systems. Another advantage of all optical switch fabrics over the optoelectronic switch fabrics is that the all-optical switches are bit rate independent and protocol transparent.
Design Considerations
When designing all-optical switches, a designer considers various design parameters and attempts to optimize these parameters. Some of these key design parameters include, but are not limited to, low insertion loss, low crosstalk, polarization independence, high reliability, compact size, simple operation, low cost, scalability to high port count, and fast switching time.
Crossbar Architecture
FIG. 1 illustrates a prior art switch that employs an architecture that is often referred to as a crossbar architecture. A crossbar switching fabric is constructed by using N2 1xc3x972 switches, where there is one 1xc3x972 switch at each intersection between an input and an output. In this example, the 3xc3x973 switch has three inputs, three outputs, and a total of nine 1xc3x972 switches in the switching fabric.
Unfortunately, the cross bar architecture has the disadvantage that the insertion loss of the longest path through the switch increases with the number (N) of inputs and outputs. The loss of the shortest path through the switch remains constant with N, so the difference in loss between the shortest and longest path also increases with N.
3D MEMS
FIG. 2 illustrates a prior art switch matrix that uses a 3-dimensional micro-ElectroMechanical System (3D MEMS). This approach employs micromirror switch elements steerable in an analog fashion in two dimensions. Each micromirror acts as a 1xc3x97N switch. An example of this approach is described in xe2x80x9c1296-port MEMS transparent optical crossconnect with 2.07 Petabit/s switch capacity,xe2x80x9d by R. Ryf et al., paper PD28, Conference on Optical Fiber Communications, OFC 2001, Anaheim Calif., USA.
One advantage of this prior art switch is that as N (number of ports) increases, the optical insertion loss of the fabric in general increases only gradually because the loss of the 1xc3x97N or Nxc3x971 switch increases only gradually with N. Another advantage of this approach is that the interconnection between the input stage of N(1xc3x97N) switches and the output stage of N(Nxc3x971) switches is performed in free space, thereby avoiding a xe2x80x9cfiber junglexe2x80x9d (i.e., the N2 connections between the input and output stages).
One disadvantage of this prior art approach is that a careful and usually expensive mechanical design is necessary to maintain alignment and minimize loss. It is noted that alignment must be maintained even in the face of vibration and temperature variations, which complicates the design. In the 3D MEMS fabric, this disadvantage is amplified by the analog nature of the micromirrors, which are also sensitive to vibration and temperature changes. Typically a large (e.g., greater than 100 ports) 3D MEMS switch requires closed-loop control for each mirror, which, as can be appreciated, increases the cost to manufacture the switch and degrades the reliability of the switch.
Another disadvantage of this prior art approach is that the physical size, complexity, and cost of the fabric increases strongly with N because more ports means that the unguided beam must travel further between input and output. To allow this, the collimated beam must either be re-collimated along its path, thereby requiring that expensive optics be precisely placed to avoid loss; or a larger beam diameter must be used, thereby further increasing the physical size of the fabric.
Consequently, it is desirable for there to be an architecture of an optical switch that simultaneously provides permanent alignment, low loss, compactness and simple interconnect.
Based on the foregoing, there remains a need for an optical switch with a geometry based on perpendicularly-oriented planar lightwave circuit switches that overcomes the disadvantages set forth previously.
According to one embodiment of the invention, an optical switch that has a plurality of input ports and a plurality of output ports is described. The optical switch features a fan-out in architecture has a fan-out stage, a fan-in stage, and a coupling mechanism. The fan-out stage is coupled to the plurality of input ports and has a first orientation. The fan-in stage is coupled to the plurality of output ports and has a second orientation. The coupling mechanism optically couples the fan-out stage with the fan-in stage and maintains a predetermined relationship between the first orientation of the fan-out stage and the second orientation of the fan-in stage.
According to another embodiment of the invention, an optical switch that has a plurality of input ports and a plurality of output ports is described. The optical switch includes a group of fan-out switches that is coupled to the plurality of input ports and a group of fan-in switches coupled to the plurality of output ports. The fan-out switches are stacked in a first set of planes in a first orientation that is substantially parallel to a first reference plane. The group of fan-in switches is stacked in a second set of planes in a second orientation that is substantially parallel to a second reference plane. The first reference plane is in a predetermined orientation with respect to the second reference plane. For example, the first reference plane may be substantially orthogonal to the second reference plane.